Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$89.48	10.294%	$98.6911	$98.69	$98.70	$98.70
Purchase #2	$218.90	6.580%	$233.3036	$233.30	$233.30	$233.30
Purchase #3	$45.51	4.605%	$47.6057	$47.61	$47.60	$47.60
Purchase #4	$179.52	4.747%	$188.0418	$188.04	$188.05	$188.00
Purchase #5	$96.34	9.851%	$105.8305	$105.83	$105.85	$105.80
Purchase #6	$128.83	6.788%	$137.575	$137.58	$137.60	$137.60
Purchase #7	$158.40	9.231%	$173.0219	$173.02	$173.00	$173.00
7 purchase totals =	$916.98		$984.0696	$984.07	$984.10	$984.00